triprotic acid

(noun)

one that can donate three hydrogen ions per molecule during dissociation

Related Terms

Examples of triprotic acid in the following topics:

  • Polyprotic Acid Titrations

    • Certain types of polyprotic acids have more specific names, such as diprotic acid (two potential protons to donate) and triprotic acid (three potential protons to donate).
    • Likewise, a triprotic system can be envisioned.
    • An example of a triprotic acid is orthophosphoric acid (H3PO4), usually just called phosphoric acid.
    • Another example of a triprotic acid is citric acid, which can successively lose three protons to finally form the citrate ion.
    • Triprotic acids can make three distinct proton donations, each with a unique Ka.

  • Diprotic and Polyprotic Acids

    • As their name suggests, polyprotic acids contain more than one acidic proton.
    • Two common examples are carbonic acid (H2CO3, which has two acidic protons and is therefore a diprotic acid) and phosphoric acid (H3PO4, which has three acidic protons and is therefore a triprotic acid).
    • A triprotic acid (H3A) can undergo three dissociations and will therefore have three dissociation constants: Ka1 > Ka2 > Ka3.
    • Take, for example the three dissociation steps of the common triprotic acid phosphoric acid:
    • Identify the key features that distinguish polyprotic acids from monoprotic acids.

  • Phosphorus Compounds

    • Hypophosphorous acid, H3PO2, contains one acidic OH bond and two (relatively) non-acidic PH bonds.
    • Phosphorous acid, H3PO3, contains two acidic OH bonds and one PH bond.
    • Orthophosphorous acid, also written H3PO3, contains three acidic OH bonds and no PH bonds.
    • Orthophosphoric acid, H3PO4, is the parent acid and most common oxidation state of phosphorus, with three acidic OH protons .
    • Since it is triprotic, phosphoric acid converts stepwise to three conjugate bases:

  • Acid Dissociation Constant (Ka)

    • The acid dissociation constant (Ka) is the measure of the strength of an acid in solution.
    • The acid dissociation constant (Ka) is a quantitative measure of the strength of an acid in solution.
    • Acid dissociation constants are most often associated with weak acids, or acids that do not completely dissociate in solution.
    • Acids with a pKa value of less than about -2 are said to be strong acids.
    • Acetic acid is a weak acid with an acid dissociation constant $K_a=1.8\times 10^{-5}$ .

  • Strong Acids

    • The strength of an acid refers to the ease with which the acid loses a proton.
    • where HA is a protonated acid, H+ is the free acidic proton, and A- is the conjugate base.
    • Strong acids yield weak conjugate bases.
    • For sulfuric acid, which is diprotic, the "strong acid" designation refers only to the dissociation of the first proton:
    • p-Toluenesulfonic acid is an example of an organic soluble strong acid, with a pKa of -2.8.

  • Weak Acids

    • The majority of acids are weak.
    • Examples of weak acids include acetic acid (CH3COOH), which is found in vinegar, and oxalic acid (H2C2O4), which is found in some vegetables.
    • Acids with a Ka less than 1.8×10−16 are weaker acids than water.
    • The Ka of acetic acid is $1.8\times 10^{-5}$.
    • Although it is only a weak acid, a concentrated enough solution of acetic acid can still be quite acidic.

  • The Brønsted-Lowry Definition of Acids and Bases

    • Originally, acids and bases were defined by Svante Arrhenius.
    • A wide range of compounds can be classified in the Brønsted-Lowry framework: mineral acids and derivatives such as sulfonates, carboxylic acids, amines, carbon acids, and many more.
    • The conjugate acid is the species that is formed when the Brønsted base accepts a proton from the Brønsted acid.
    • Here, acetic acid acts as a Brønsted-Lowry acid, donating a proton to water, which acts as the Brønsted-Lowry base.
    • Chemistry 12.1 What are Acids and Bases?

  • Oxoacids

    • Halogen oxoacids include hypochlorous acid (HOCl); chlorous acid(HOClO); chloric acid(HOClO2); oerchloric acid(HOClO3); oerbromic acid (HOBrO3)
    • Consider the simple oxyacids HOI (hypoiodous acid), HOBr (hypobromous acid), and HOCl (hypochlorous acid).
    • The strongest acid is perchloric acid on the left, and the weakest is hypochlorous acid on the far right.
    • Carboxylic acids are the most common type of organic acid.
    • Mellitic acid is an example of a hexacarboxylic acid.

  • Carboxylic Acids

    • Carboxylic acids are organic acids that contain a carbon atom that participates in both a hydroxyl and a carbonyl functional group.
    • As proton donors, carboxylic acids are characterized as Brønsted-Lowry acids.
    • Salts and esters of carboxylic acids are called carboxylates.
    • Generally, in IUPAC nomenclature, carboxylic acids have an "-oic acid" suffix, although "-ic acid" is the suffix most commonly used.
    • Carboxylic acids are characterized as weak acids, meaning that they do not fully dissociate to produce H+ cations in a neutral aqueous solution.

  • Naming Acids and Bases

    • Simple acids, known as binary acids, have only one anion and one hydrogen.
    • So, HNO3 will be nitric acid.
    • Therefore, HClO4 is called perchloric acid.
    • For example, chlorous acid is HClO2.
    • For example, instead of bromic acid, HBrO3, we have hypobromous acid, HBrO.